1. Field of the Invention
The present invention relates to acrylic pressure-sensitive adhesive compositions. Specifically, it relates to pressure-sensitive adhesive compositions that excel in adhesiveness to glass and transparent plastics such as polyacrylates, polycarbonates, poly(ethylene terephthalate)s (PETs), resistance to blistering/separation, transparency, and coatability and do not cause corrosion typically on thin metal films. Additionally, it relates to pressure-sensitive adhesive articles bearing the pressure-sensitive adhesive compositions, and displays as affixed using the pressure-sensitive adhesive articles.
2. Description of the Related Art
Flat panel displays (FPDs) typified by liquid crystal displays (LCDs) have been used more and more. Such flat panel displays are fabricated by laminating optical films having various functions through pressure-sensitive adhesives (tacky adhesives). Pressure sensitive adhesives for use in these applications should have excellent reliabilities in addition to satisfactory adhesiveness and transparency. Typically, they should suffer from no blister and separation (have resistance to blistering/separation) under conditions at high temperatures and/or high humidity (high-temperature/high-humidity conditions).
Exemplary known techniques for improving the resistance of pressure-sensitive adhesives to blistering/separation under conditions at high temperatures and/or high humidity include techniques of allowing the pressure-sensitive adhesives to have higher glass transition temperatures (Tg) typically by copolymerizing with monomers whose homopolymers have high glass transition temperatures (Tg) (monomers having high glass transition temperatures (Tg)) or with monomers containing a functional group such as carboxyl group; and by adding oligomers (low-molecular-weight polymers) thereto.
Typically, Japanese Patent No. 3516035 discloses a pressure-sensitive adhesive composition which contains a polymer including a carboxyl-containing monomer as a component; and an oligomer including an amino-containing monomer as a component and which excels in adhesiveness to plastics and in resistance to blistering at room temperature (ordinary temperature) and at high temperatures. Japanese Unexamined Patent Application Publication (JP-A) No. 2001-89731 discloses a pressure-sensitive adhesive composition which contains a (meth)acrylate polymer (A) having a weight-average molecular weight of 50×104 to 250×104 and another (meth)acrylate polymer (B) having a weight-average molecular weight of 5000 to 50×104 in a specific weight ratio, in which one of the (meth)acrylate polymers (A) and (B) has a nitrogen-containing functional group. Additionally, JP-A No. 2002-327160 discloses a pressure-sensitive adhesive composition which contains 100 parts by weight of a pressure-sensitive adhesive polymer as a copolymer of an alkoxyalkyl (meth)acrylate as a main component and a carboxyl-containing monomer; 5 to 40 parts by weight of a low-molecular-weight polymer as a copolymer of one or more monomers, as main components, selected from alkyl methacrylates, cycloalkyl methacrylates, benzyl methacrylate, and styrene with an amino-containing or amido-containing monomer; and 0.001 to 2.0 parts by weight of a crosslinking agent. This document also discloses a pressure-sensitive adhesive sheet using the pressure-sensitive adhesive composition.
These pressure-sensitive adhesive compositions, however, suffer from insufficient adhesive properties at low temperatures or under high-speed conditions, because their pressure-sensitive adhesives have high glass transition temperatures (Tg). Among them, the pressure-sensitive adhesive composition containing a carboxyl-containing monomer suffers from insufficient anticorrosive properties when it is applied to thin metal films (inclusive of thin metal oxide films). Specifically, there has been obtained no pressure-sensitive adhesive composition which is excellent and satisfactorily has all characteristic properties such as resistance to blistering/separation under conditions at high temperatures and/or high humidity, adhesive properties at low temperatures, and anticorrosive properties at high levels.